This research proposes to identify the mechanism(s) of thromboembolic complications, e.g., intravascular coagulation, thrombolic sequelae of heart valve diseases, and cerebral vein thrombosis caused by biologic agents which contribute to an estimated 18,000 deaths per year due to gram-negative sepsis alone. We propose to clarify the cellular sequence of events involved in the pathogenesis of these complications and to develop quantitative methods for measuring membrane receptors and cellular factors interacting with the blood clotting system. In human platelets, granulocytes, and endothelial cells we will measure the attachment of biologic agents, endotoxin and the staphylococcal Protein A-IgG complex, and we will clarify the pathomechanism of cell injury by studying changes in membrane associated procoagulant, tissue factor activity, and lysosomal enzymes. Using a novel immunologic method developed in this laboratory we will study heparin-neutralizing factors and substances elaborated by human cells that are important in clot formation. Cellular fractionation, isotope techniques, immunochemical, and enzymological determinations will be employed. Our work will continue on the molecular mechanism of the interaction between human fibrinogen and staphylococci applied by us as a laboratory tool for the diagnosis of intravascular coagulation, acute pulmonary thromboembolism, and detection of abnormal variants of fibrinogen. This line of research will involve further characterization of the binding site for staphylococci and streptococci on the polypeptide chain subunits of human fibrinogen. The results of the proposed experiments should contribute to the elucidation of cellular and humoral changes induced by biologic agents and responsible for thromboembolic complications.